A. Field of the Invention
This invention relates generally to printing devices, and more particularly to hand-held labelers utilizing circuitry accurately to determine the position of the printing web, and to control the operation of the printing head, preferably a thermographic printing head, in response to position signals to thereby accurately position the imprints on the web.
B. Prior Art in the United States
Hand-held labelers utilizing thermographic printing devices are known. Examples of such hand-held labelers are illustrated in U.S. Pat. No. 4,264,396 to Stewart, U.S. Pat. No. 4,407,692 to Torbeck and U.S. patent application Ser. No. 485,012 filed Apr. 14, 1983.
While the devices disclosed in the abovedescribed references do provide a way to make imprints on a thermosensitive web, they do not contain certain of the features provided by the device of the present invention. For example, when printing with a thermal printing device, particularly with a high density printing device such as one of the devices illustrated in the aforementioned Pat. No. 4,407,692 and application Ser. No. 485,012, it is necessary accurately to control the timing of the energization of the various printing elements as a function of the position of the web. For example, in such a system, the web is continously fed, and the appropriate printing elements must be energized at the precise time that the portion of the web on which the imprinting is desired is positioned adjacent the printing head. The difficulty of the problem is further compounded by the fact that each of the printing elements has a length and a width of only a few mils. As a result, the position of the web or the timing of the energization of the printing elements, must be precisely controlled to avoid printing gaps and changes in print density, as well as changes in character shape, particularly when the speed of the web varies as it passes the printing head, as for example, in the case of a labeler having a hand advanced web.